1. Technical Field
The present invention relates to a head which ejects a liquid, and a liquid ejecting apparatus which is provided with the head, and particularly relates to an ink jet recording head and an ink jet type recoding apparatus which eject ink as the liquid.
2. Related Art
A piezo ink jet system is an on-demand type ink jet printing system which discharges a liquid droplet by deforming a piezo element through the applying of a voltage to the piezo element (JIS Z8123-1: 2013).
A permanent head is a machine portion or an electrical portion of a printer main body which continuously or intermittently generates a liquid droplet of ink (JIS Z8123-1: 2013).
The permanent head (hereinafter, referred to as a “head”) which is used in the piezo ink jet system is provided with a channel formation substrate on which a pressure generating chamber, which communicates with a nozzle for ejecting a liquid droplet is formed, a piezo element which is provided on one surface side of the channel formation substrate, and a driving circuit board in which a driving circuit, which is bonded onto the channel formation substrate so as to be close to the piezo element and drives the piezo element is provided. The permanent head ejects the liquid droplet from the nozzle by driving the piezo element by the driving circuit and applying a pressure change to the liquid in the pressure generating chamber.
As the piezo element described above, a thin-film type piezo element which is formed on the channel formation substrate through a film formation method and a lithography method has been proposed. When using such a thin-film type piezo element, it is possible to dispose the piezo element at high density; however, it is difficult to electrically connect the piezo element which is disposed at high density and the driving circuit.
For this reason, there have been suggested a configuration such that a bump is provided on the driving circuit board, and the driving circuit and the piezo element are electrically connected to each other via the bump (for example, JP-A-2014-51008).
In this way, by using the bump for connection between the driving circuit and the piezo element, it is possible to ensurely connect the piezo element which is disposed at high density and the driving circuit at low cost.
In addition, the driving circuit board and the channel formation substrate are bonded to each other via an adhesive layer which is provided around the bump. The bump and the adhesive layer have a certain height, and a holding portion which is a space for accommodating a piezo element is formed between the driving circuit board and the channel formation substrate.
However, there is a problem in that if the holding portion does not have sufficient height, the piezo element is displaced and comes in contact with the driving circuit board such that the displacement of the piezo element is disturbed. In addition, it is considered that the height of the bump and the adhesive layer is set to be larger than a certain height so as to secure the sufficient height of the holding portion; however, since it is difficult to maintain the strength, there is a limit to the height of the bump and the adhesive layer.
Further, when the height of the bump and the adhesive layer is set to be larger than a certain height so as to secure the height of the holding portion, the width of the bump and the adhesive layer is required to be larger, and a space for disposing the bump and the adhesive layer is also required, which brings about a problem in that the driving circuit board is enlarged.
In addition, when the holding portion does not have the sufficient height, there is a concern in that discharge is likely to occur due to a potential difference generated between the wirings which are provided on each of the driving circuit board and the channel formation substrate, and thus the driving circuit and the piezo element are destroyed.
Note that such a problem exists in not only an ink jet recording head, but also a head for ejecting liquid droplets other than the ink.